Plural chambered, oscillator-coaxial line resonator-detector assembly for moving object detection systems

ABSTRACT

A plural chambered assembly for electromagnetic moving object detection systems. One chamber forms the outer conducting surfaces of a cavity resonator having a centrally disposed conductor short-circuited at one end to the conducting surfaces and open at the other end. Collectively the center conductor and outer conducting surfaces define a coaxial line resonator. A rectifier and rectifier load are electrically connected to the center conductor and physically mounted within the cavity chamber. A second contiguous chamber houses a solid-state, sinusoidal, continuous wave oscillator. A radiator is capacitively coupled to the center conductor of the coaxial line resonator.

gutted States Patent :72] Inventor George Boyko Fruulngham, Mass.

{21] Appl No. 733,672

[22] Filed May 31.1968

[451 Patented Aug. 10.1971

173] Assignee Pinkertons. Incorporated New York, N.Y.

{541 PLURAL CHAMBERED, OSCILLATOR-COAXIAL LINE RESONATOR-DETECTORASSEMBLY FOR MOVING OBJECT DETECTION SYSTEMS 5 Claims, 4 Drawing Figs.

[52] US. Cl .0 340/258,

(51 Int. Cl. ..,....G08b1 3/ 22 GOls 9/44, 1103f 3/60 [50] Field ofSearch ..340/258, 25

A, 25C; 343l702,900, 8-, 330/56; 331/96, 97, 101-, 334/45 [56]References Cited UNlTED STATES PATENTS 2,161,707 6/1939 Hathaway 343/900X 2,859,434 11/1958 Auer,Jr.eta1..t. 343/8 3,162,823 12/1964 Beaty 1/101X 3,210,752 10/1965 Bojkow 340/258 3,270,292 8/1960 Harwood 334/45 X3,307,099 2/1967 Weller et a1. 334/45 UX 3,440,650 4/1969 Kimball l340/258 3,470,476 9/1969 Wilson 3 1/101 X 3,246,266 4/1966 331/101 XRacy Primary Examinen-John W. Caldwell Assistant Examiner- Perry PalanAtrorney-RusselL Chittick & Pfund ABSTRACT: A plural chambered assemblyfor electromagnetic moving object detection systems One chamber formsthe outer conducting surfaces of a cavity resonator having a centrallydisposed conductor short-circuited at one end to the.

conducting surfaces and open at the other end. Collectively the centerconductor and outer conducting surfaces define a coaxial line resonator.A rectifier and rectifier load are electrically connected to the centerconductor and physically mounted within the cavity chamber. A secondcontiguous chamber houses a solid-state,'sinusoidal, continuous waveoscillator. A radiator is capacitively coupled'to the center conductorof the coaxial line resonator.

PATENTEDAUBIOBH 9599.196 I SHFETIOFZ INVENTOR.

BY GEORGE BOYKO PATENTEUMJGIOIQYI 3.599.196

SHEET 2 OF 2 5O 52 60 I 62 I 94 9+ REGULATED 6 mg INVENTOR.

GEORGE BOYKO BY PLURAL CHAMBERED,.OSCILLATOR-COAXIALLINERESONATOR-DETECTOR ASSEMBLY FOR MOVING OBJECT DETECTION SYSTEMS CROSSREFERENCES TO RELATES APPLICATIONS The subject matter of the presentapplication is related to the ElectromagneticMoving Object DetectionSystem Utilizing A Coaxial Line Resonator and Alarm System described inmy copending'applications Ser. No. 733,673, filed'May3l, 1968 and Ser.No. 733,671,-filed May 31, I963", respectively.

BACKGROUND OF THE INVENTION In existing'moving objectdetection systemsof the type having one'or more remote antennas and a central controlunit, the remote antennas are'generally'driven by acorrespondjng numberof oscillators housed inthe central control unit. In some instances, tworemote antennas aredriven by a single oscillator in the control unit.lfmorethan one'pair ofantennas is required to cover the desiredprotection area, an additional oscillator is added at the control unitfor-each pair of additional antennas. The remotely located antcnnasareconnected to the oscillators in the central control unit by coaxialcable. This arrangement presents a number of problems including signalattenuation along the coaxial cable, false alarms caused by motion ofthe cable, limitations on the separation distance between theremoteantennas; and thecentrel control unit-end the genera] expenseofinstalling thecoaxial cable.

It is accordingly ageneral object of the present invention to provide aunitary, oscillator-antenna assembly that can be used as a remote'sensorwithout requiring a coaxial cable-connection between the assembly andthe central control unit.

It is a specific object of the present invention to provide a unitary,plural chambered, oscillator-coaxial line resonator detectorassembly-for electromagnetic movingobject detection systems.

It is a feature of the invention that the twoassembly chambers arecontiguous and share a common walLThis feature allows a very small leadlength between the oscillator circuit housed in one chamber andthecoaxial line-cavity formed by the other chamber. In addition, itprovidesa low packaging profile forthe entire assembly.

These objects and other objects and features of the present inventionwill best be understood from a preferred embodiment thereof, selectedfor purposes of illustration, and shown in theaccompanying drawings inwhich:

:FIG. I is an isometric view of the assembly showing'the antenna,housing and baseplate;

FIG. 2 is a partial schematic and block diagram of the electricalcircuitry of the oscillator, coaxial line resonator and'detectorhoused'within the assembly shown in FIG. 1;

FIG. 3 is a bottom view of the assembly with the bottom plate removedand a portion oftheassembly broken away; and,

FIG. 4 is an-exploded-view in partial cross section showing thephysicalv mounting and electricalcoupling of the antenna to the centerconductorof the coaxial line'resonator.

Turning now to the drawings, and particularly to FIG. 1 thereof, thereis shown in isometric view, a plural chambered, oscillatoncoaxial lineresonator-detector assembly constructed in accordance with the presentinvention and indicated generally by the reference number 1. The majorcomponents of the assembly 'lflthat are visible in=FIG. l are a bottomor baseplate 12, a generally'rectangular hosing '14, an antenna.l6 andan antenna mounting insulator 18. Before discussing indetailthephysicalconstruction and mounting of the components within thehousing ,as illustrated in'FIG..3, it will be helpful to briefly discusstheelcctrical circuitry of the oscillator-coaxial lineresonator-detector assembly.

Looking at FIG. 2, there is shown a tunable oscillator 20 which employsasingle, grounded base NPN transistor-22 to generate thecontinuousysinusoidal waves that excite coaxial line resonator 24. Atypical operating frequency for oscillator '20 is 400 megahertz. Ofcourse, other frequencies generally in the UHF range can be used inmoving object detection systems. RF ground for the base of transistor 22is established bya capacitor 26 that shunts base resistor 28. The baseresistor 28, together with resistor'30 forms a bias voltage divider from8* regulated to ground. Emitter resistor 32 provides a DC feedback pathfor oscillator stabilization while RF feedback is prevented by a shuntcapacitor 34 which places a'RF ground at the bottom ofradiofrequencychoke 36. Coupling of the generated radiofrequency energy to the powersupply (not shown) is prevented by a second radiofrequency choke 38 inthe collector circuit.

The required in-phase RF feedback to sustain oscillation is provided bythe collector-base and emitter-base capacitances. The frequencydetermining components of the oscillator com prise inductor 40, variablecapacitor 42 and a portion of the coaxial line center conductor 44. Theoscillator frequency is tuned by varying the series capacitance of thefrequency determining circuit. This is accomplished by adjusting thevariable capacitor 42'. I

Coaxial line resonators of the type illustrated in'FIG. 2 arenow'g'enerally classified cavity resonators/Henney, Radio EngineeringHandbook, 5th Edition, page 6-46. Conceptually, the coaxial lineresonator 24 can be regarded as a coaxial tran'smksion lineshort-circuited at one end and open at the other. Terman, Electronic andRadio Engineering, 4th Edition, pages l59-l61. The coaxial lineresonator is capacitively loadedand'tuned by a variable capacitor-46located at the open end of the line. This location provides the greatesttuning effect per unit of capacitance, but other locations along thecenter conductor 44 can be utilizedfor thevariable capacitor 46.

Physically, the coaxial line resonator or cavity can have a true coaxialconstruction, i.e., inner-and outer cylindricalconductors with a commonaxis or a hybrid configuration. The

present invention utilizes a hybrid or trough line configuration thathas a center conductor positioned within a rectangular prism cavity. Therectilinear configuration ofthe coaxial line" resonator of the'presentinvention is more desirable than the classic cylindrical configurationbecause it simplifies mechanical fabrication production line assemblyand component mounting.

The term coaxial line has been selected to describe the resonator orcavity 24 because it connotes a centrally disposed conductor surroundedby one or more conducting surfaces. This is true even though thedefinedcavity may have a rectangularshape of the type shown in "FIG. 3. As usedherein, the

term coaxial line'resonator" shall mean a resonant cavity centerconductor 44 of the resonator. The coupling should be as looseaspossible within the limits imposed by the desired detection range. Theloose coupling of the oscillator to the high Q coaxial line resonatorcircuit effectively isolates the oscillator from motion producedimpedance changes in the antenna circuit thereby maintaining thefrequency stability of the-oscillator.

Thecoaxial line resonator 24 is constructed with the center conductor 44having a physical length that is less than /4 l\ at the operatingfrequency. The electricallength of the line is ad justed by varyingcapacitor 46. The output from the coaxial line resonatoriscapacitivelycoupled through capacitor 50 to radiator .16. Theradiatonwhich has a'length between /4 It and /2 A, is voltage fed toachieve maximum detection sensitivity. lt can beam from FIG. 2, that theoutput from the coaxial line resonator is taken at a point52 that isvery close to the .point ofmaximum voltage on the center conductor 44.

Changes in the impedance of the antenna circuit produced by motion of anobject within the radiated field pattern of the alarm system are sensedby a rectifier $4. The rectifier is connected to the centerline 44 ofthe coaxial line resonator at a point 56 located slightly below theoutput tap 52 for the amen na. The connection point for the rectifier isa compromise between achieving maximum voltage output and minimum effectupon the Q of the coaxial line resonator. A load for the rectifier 54 isprovided by resistor 58.

The detected motion signals from rectifier 54 are capacitively coupledthrough capacitor 60 to a high gain, low frequency amplifier 62. Afteramplification, the motion or alarm" signal is used to activate asuitable, electrical, visual and/or audible alarm means 64. A rangecontrol, illustrated representationally by adjustable knob 66, isprovided in the amplifier circuit to preset the range within whichmotion of an object will trigger the alarm system.

With the exception of the coupling capacitor 60, amplifier 62 includingthe range control 66 and the alarm 64, all of the previously discussedelectrical components are mounted within or on the assembly housing 14.If desired, the rectifier 54 and rectifier load resistor 58 can bemounted outside of the chamber 82. The components are identified in FIG.3 by the same reference numerals that were used in the partial schematicand block diagram of FIG. 2. The basic structure of the housing 14 isillustrated in the isometric and bottom view: of FIGS. 1 and 3,respectively. The rectilinear housing is formed from two end walls 68and 70, two sidewalls 12 and 74, a top plate 76 and the removable bottomor baseplate 13. The walls and top plate are constructed from anelectrically conductive material, such as, cadmium plated steel oraluminum, and are joined together, as by soldering, to form a pluralityof continuous electrically conductive surfaces. The bottom plate 12 isalso made of an electrically conductive material and, when removablysecured to the housing by screws 78, completes the shielding of thecomponents within housing 14.

Looking specifically at FIG. 3, a longitudinal, electrically conductivecenter wall 80 divides the interior of the housing 14 into two generallyrectangular chambers 82 and 84. It can be seen that when the bottomplate 12 is screwed to the housing 14, the continuous electricallyconducting surfaces of the end walls 68 and 70, top and bottom plates 76and 12. and center wall 80 will produce the cavity" portion of thecoaxial line resonator 24. Thiscavity or chamber 82 together with thecenter conductor 44 electrically comprise the coaxial line resonator 24.

The center conductor 44 is physically mounted on and electricallyshort-circuited to one of the conducting surfaces that form the resonantcavity, in this case, end wall 68, The other end of the conductor isopen and capacitively loaded by variable capacitor 46. The centerconductor is current fed from oscillator at tap point 48. Physically,the oscillator tuning variable capacitor 42 is located partially incavity chamber 82 and partially in the oscillator circuit chamber I4. Anaperture 86 in the center wall 80 provides mounting room for thevariable capacitor. Access to the variable capacitor trimmer screw 88 isprovided by an aperture 90 in the housing end wall 68, as shown in FIG.1.

The physical dimensions of the in general, and the coaxial lineresonator in particular, will vary depending upon the operatingfrequency of the oscillator 20. 'At a nominal frequency of 400megahertz, the cavity or chamber ll of the coaxial line resonator isapproximately 3 96 inches long and has a square end profile of VIXVBinches. The center conductor 44 is formed from a l/l6-inch strip of thesame or similar electrically conductive material and has a length ofapproximately 3 inches. The dimensions of chamber 84 are not criticalbecause the chamber functions only as a mounting area andelectromagnetic shield for the oscillator components. However, for easeof assembly and fabrication. the opcillator chamber 84 is madeapproximately the same size as the resonator chamber 82.

It has already been mentioned that the antenna 16 is capacitivelycoupled to the center conductor 44 through capacitor 50. Electrically,the coupling capacitor 50 can be considered as a separate circuitcomponent. However, from a physical standpoint, the coupling capacitoris not a separate component, but instead is formed by the mountingcomponents for the antenna. The antenna mounting system is shown inpartial cross section in FIG. 4. The antenna 16 is screwed onto athreaded stud 92 that extends through, but is electrically insulatedfrom the top plate 76 and the center conductor 44 of the coaxial lineresonator 24. The threaded stud is insulatively secured to the centerconductor 44 by an insulative nut 94 and shoulder washer 96. A metal nut98 completes the assembly with respect to the center conductor.Capacitive coupling occurs between the center conductor 44 and stud 92and nut 98 with the insulative shoulder washer 96 acting as thedielectric material.

The stud 92 is fixed with respect to and insulated from the top plate bythe following components viewed from bottom to top in FIG. 4: nut 100,insulative washer 102, antenna insulator insert 104, insulative washers,e.g., cork 106 and 108, antenna insulator l8, insulative washer 110,metal flat washer 112 and nut 114. It will be appreciated'that thisconstruction provides the necessary electrical coupling between thecoaxial line resonator and antenna while at the same time producing amechanically secure and rigid assembly of the antenna and resonatorcomponents.

A number of variations in the design of the plural chambered assembly 10are possible. For instance, the size of the baseplate 12 is not criticalas long as it is large enough to completely cover both of the chambers82 and 84. Preferably the baseplate is made large enough to accommodatea housing (not shown) for the circuit components that comprise amplifier62. If desired, the amplifier housing and the oscillator-coaxial lineresonator-detector assembly can be provided with a common cover (notshown) to produce a unitary, visually pleasing remote sensor unit. Itwill be appreciated that since the oscillator, coaxial line resonator,antenna and detector comprise a single sensor unit, no coaxial cable isrequired between the sensor unit and the central control unit.Furthermore, ordinary wiring can be used for the power and alarmcircuits between each remote sensor unit and the control or alarm unit.

Having described in detail a preferred embodiment of the pluralchambered, oscillator-coaxial line resonator-detector assembly formoving object detection systems, it will now be apparent to thoseskilled in the art that numerous modifications can be made theretowithout departing from the scope of the present invention,

What I claim and desire to secure by United States Letters Patent is:

l. A plural chambered, oscillator-coaxial line resonator-detectorassembly for electromagnetic moving object detection systems comprising:

housing means for providing two chambers one of which has a plurality ofconducting surfaces defining a rectangular resonant cavity;

a centrally disposed, substantially planar strip conductor mountedwithin said cavity, said conductor being short-circuited at one end ofone of the conducting surfaces and open at the other end;electromagnetic oscillator means mounted within the other chamber ofsaid housing and loosely coupled to said cavity conductor;

an antenna insulatively mounted on said housing means and having anelectrically conductive extension member that extends through anaperture in said strip conductor and is separated therefrom by a soliddielectric material, said strip conductor, dielectric material andextension member forming a coupling capacitor between said conductor andsaid antenna; and,

detector means connected to said cavity conductor.

2. The assembly of claim 1 wherein said housing means comprises:

first and second end and sidewalls and a top plate secured together toform a plurality of continuous, electrically conductive surfaces; anelectrically conductive center wall secured to said end walls and saidtop plate, said center wall defining two chambers one of which forms arectangular cavity resonator; and

i an electrically conductive bottom plate removably secured to saidside, end and center walls to close and electrically shield saidchambers.

1. A plural chambered, oscillator-coaxial line resonatordetectorassembly for electromagnetic moving object detection systems comprising:housing means for providing two chambers one of which has a plurality ofconducting surfaces defining a rectangular resonant cavity; a centrallydisposed, substantially planar strip conductor mounted within saidcavity, said conductor being short-circuited at one end of one of theconducting surfaces and open at the other end; electromagneticoscillator means mounted within the other chamber of said housing andloosely coupled to said cavity conductor; an antenna insulativelymounted on said housing means and having an electrically conductiveextension member that extends through an aperture in said stripconductor and is separated therefrom by a solid dielectric material,said strip conductor, dielectric material and extension member forming acoupling capacitor between said conductor and said antenna; and,detector means connected to said cavity conductor.
 2. The assembly ofclaim 1 wherein said housing means comprises: first and second end andsidewalls and a top plate secured together to form a plurality ofcontinuous, electrically conductive surfaces; an electrically conductivecenter wall secured to said end walls and said top plate, said centerwall defining two chambers one of which forms a rectangular cavityresonator; and an electrically conductive bottom plate removably securedto said side, end and center walls to close and electrically shield saidchambers.
 3. The assembly of claim 1 further characterized by tuningmeans connected to said cavity conductor.
 4. The assembly of claim 3wherein said tuning means comprises a variable capacitor connectedbetween the open end of said cavity conductor and one of said conductingsurfaces.
 5. The assembly of claim 1 wherein said detector meanscomprise a rectifier and a rectifier load resistor mounted within saidcavity.